Sequential switching system



July 30, 1963 A. ELOVIC SEQUENTIAL SWITCHING SYSTEM Filed May 10. 1961 N%E w 5&3 m muaomdd v A/JDOr v o I mI 8 :1 & NIY I. +000 H +H 3 OOWO VF5050 JOtFZOO INVENTOR. Alexander ElOVIC BY M ATTORNEYS.

United States Patent C) 3,099,787 SEQUENTIAL SWITCHING SYTEM AlexanderElovic, Elizabeth, N.J., assignor to Indiana General Corporation,Valparaiso, End, a corporation of Indiana Filed May 10, 196i, Ser. No.119,763 13 Claims. (Cl. 321-45) This invention relates to electronicswitching systems and more particularly relates to fast-actingsequential switching circuitry.

When transformers are used in high-speed pulsed or switching circuits,the rate of sequencing or successive pulsing of the transformers islimited by their recovery time needs. This factor substantially reducesthe potential circuit speed of operation. In accordance with the presentinvention, at least two control branches are successively triggered intoa common load or output.

With a control transistor and a pulse or output transformer in eachbranch, their utilization in rapid alternate sequence providessuccessive sequential control operation for the common output. Eachoutput transformer fully recovers during its successive reset ornon-operative cycles. The load is therefore directly sequentially pulsedor controlled with no time lag, namely, with an eiiective zero recoverycircuit. This results in a high repetition rate of control, independentof transformer recovery time. The use of output transformers in theinvention arrangement provides ready current or voltage ratiotransformation to the load, as desired.

The invention control system, in operating the output transformers forno more than 50% of the control periods, thereby distributes the loadbetween them. In this mannor, the units cool oil, as well as recover,between alternate control pulses. The result is eflicient, effective andfast control operation, with load sharing by the transformers. Theindividual transformer design is thus less costly as compared to designsfor fast repetition response. In a similar manner, the branch controltransistors share the load of the control operation. This results in theeffective use of cheaper types, as germanium, as against silicon, forrapid sequencing.

Another important feature and advantage of the present invention is thestabilization of the power supply operation and demand by the branchedcontrol system hereof. The overall current requirement of the system ismade substantially constant by novel control Steering of the transistorcurrents among the circuit sections. This results in a negligible rippleand transients in the power supply section, reducing the cost and andweight of its filtering.

It is accordingly, a primary object of the present invention to providea novel fast-acting sequential switching system, one with a rapidrepetition rate.

Another object of the present invention is to provide a novel branchedcontrol circuit with a common load or output wherein the branchcomponents successively assume and share the control load.

Another object of the present invention is to provide a novel controlcircuit with a plurality of output transformers to a common load, thatalternately assume rest status for full recovery and resultant rapidsequential output response.

Still a further object of the present invention is to provide a novelsequential control system with stabilized power supply currentoperation.

These and further objects of the present invention will become moreapparent from the following description of an exemplary embodimentthereof, illustrated in the drawing in which the sole FIGURE is aschematic circuit diagram of the exemplary sequential control circuit.

The exemplary control circuit is arranged to apply cur- 3,099,787Patented July 30, 1963 rent pulses to a load 20*, in rapid sequence ifneed be. A typical load contemplated herein is an inhibit Winding of amagnetic core matrix memory plane ofa digital computer. For half cyclesequential memory plane operation, current pulses of the order of 3microseconds duration, with negligible time separation, are desirablyapplied to the windings (20) in a controlled pattern. The inventionsystem effectuates such control operation with the use of transformers21 and 22, coupled to load winding 20. As set forth hereinafter, theoutput coupling results in uni-directional flow to the winding 20,despite alternated cycling of the transformers 21 and 22.

The exemplary control circuit contains three PNP transistors, T T and Twherein only one may be conductive at any one time. Alternatively NPNtransistors may be used with reversal of operating voltages and bias, asis understood by those skilled in the art. When no current pulse is tobe impressed on load 29, input transistor T is rendered On, with apredetermined current flowing through it, and the output transistors Tand T are cut Off. This is the standby mode of circuit operation. Acommon DC. power supply 25 contains the usual rectifier and filtersections (not shown), and is energized from a suitable A.C. source 26.

Power supply 25 has three output terminals: one (27) for +V, as 'at +22volts; one (28) for -V, as at 22 volts; and ground (29). The emitterelectrode of transistor T is connected to +V terminal 27 throughresistor 3%. Its collector is returned to the V terminal 28 throughresistor 31. A diode D is connected between the base electrode oftransistor T and system ground to provide a fixed bias to the base, as aclamp. Thus, point 32 may be normally held, e.g. at O.8 volt bias, whenno control inputs from the input AND control circuit 35 occurs. Aconstant or predetermined current i, thereby flows through transistor Tas indicated, of magnitude determined by the circuit parameters andvoltages applied by power supply 25, and the clamp diode D In thisstandby circuit mode, the control transistors T and T are in theircut-off region, and not conducting. Also, the standby voltage output ofunit 35 is negative.

When it is desired to send a signal circuit pulse into theload (20) apositive pulse or signal is applied to the base of transistor T to driveit to cut-off. This is accomplished in the exemplary circuit by and ANDcontrol unit 35. The AND circuit 35 has a plurality of input controllines 36, 36 which are individually controlled or pulsed. When all lines36, 36 receive simultaneous signals, the AND unit 35 is arranged toproduce a positive output pulse (s). Positive pulse s on input controllead 33 makes the base of transistor T sufiiciently positive to cut-oilits standby current flow i with transistor T becoming non-conductive forthe duration of the positive input signal s.

When transistor T is thus cut off by a positive input control pulse (s),the current i drops to zero. As current t recedes, the potential atcircuit point a becomes somewhat positive with respect to ground,whereupon the emitters 43 and 44 are so directly biased thereby. Theclamp D holds point a reasonably close to ground, at positive mode wheni is cut-oil. This positive value at a becomes a control signal that caninitiate an output pulse through either control transistor T or Tthrough lead 37. Which of the two branches, T or T becomes energized isdetermined by the concurrent selective biasing of their bases 41 or 42.When a base 41 or 42. is thus biased positive with respect to ground itstransistor T or T remains in the cut-oil state. However, the base 41 or42 that is at a negative voltage with respect to ground is in conditioncapable of being rendered conductive by a positive; signal impressed onits associated emitter 43 or 44.

In the exemplary circuit, the bases 41 and 42 are alternatively biasedpositively and negatively, sequentially by flip-flop unit 40. In thisway the T and T control branches, with output transformers 21 and 22,are assured of the aforesaid alternate cycle rest periods, as a minimum.Other modes of the selective biasing of bases 41 and 42 are contemplatedfor the invention system. For the rapid repetition rate or sequencingrequirements referred to, the flip-flop unit 40 is impressed with signalpulses s corresponding to those desired in the output inhibit winding20, as to duration, wave form, and succession intervals.

Alternate pulses into input 45 of flip-flop 40 results in conventiallyknown 'bi-stable operation, with output terminals A and B alternatingbetween positive and negative potential states with respect to ground.Flip-flop 40 is arranged to provide alternate +V and V at its A and Boutput terminals. When terminal A, therefore, is at V, terminal B wouldbe at +V; and vice versa, for successive similar pulse inputs .9 at 45.The s pulses at unit 40 are synchronized with the control pulses intoAND circuit 35 at input 36, 36. In this way the control action amongtransistors T T and T are coordinated for optimum action.

When terminal A is rendered negative, below ground, at V, such potentialis imparted to point 46 through limiting resistor 47. In this state, thetransistor base 41 becomes clamped to ground through diode D with base41 (at point 46) being held at a suitable negative bias, e.g. at 0.3volt. In such negatively biased mode the transistor T is in readiness tobe fired or rendered conductive if the control signal impressed upon itsemitter 43 is suitably positive. Such positive pulse or signal isprovided at point a upon the transistor T cut-ofi when AND unit 35produces the signals s, as set forth hereinabove.

With points a and b thus positive, namely at (+2), the emitter 43directly ibecomes positive. Transistor T thereby conducts for theduration of the negative state at terminal A in conjunction with theduration of circuit point b being positive. This conjoint voltage actionrenders T conductive for these stated circuit conditions, producing thelocal control branch current i Concurrently, as terminal B of unit 40 ispositive, due to the bistable circuit action of unit 40, base 42 andcircuit point 48 are positive, and transistor T is cut-off, or renderednon-conductive. The current i may be viewed as being steered from theinput transistor T branch to cross-over point b, and thence steered intothe T transistor branch as i The control current i then flows throughprimary winding 51 of output transformer 21, and back to power supply 25through common negative (V) return lead Alternatively, at the nextsuccessive pulse (6''), terminal B becomes negative, and A, positive.This state promptly cu ts off current i in branch T and makes base T andcircuit point 48 negative. Diode D clamps base 42 to ground and rendersit subject to conduction. If the T branch is simultaneously cut-off,then current i directly flows in branch T with transistor T beingconductive and signal current flowing into primary transformer winding52 and to V power return through lead 50.

When the T branch signal current i flows through primary winding 51, acorresponding current I flows in the secondary winding 53 of transformer21. Current I flows unidirectionally through diode 54- into load 24 atits terminals 55, 55 as current I Similarly, when branch T conductscurrent i through primary winding 52, the corresponding current I flowsin the secondary winding 56 of transformer 22. Current I flowsunidirectionally through diode 57 and into load 20 as the same current Iin magnitude, direction, and wave shape as from branch T Diodes 54 and57 prevent back-flow of current I and I and keep these currents directedto the common load (20). By using the same circuit elements andparameters for the T and T control abranches one insures identicaloutput signal action on the load 20, e.g., an inhibit winding, from bothsuccessively fired circuit section. Further, such balanced current andloading arrangement makes the current 1' in lead 37 constant wheneversteered therein, as it can only become i or i When the load (20) isprimarily a current responsive device, as an inhibit winding, astep-down winding ratio used at the secondary windings 53' and '56 isadvantageous. Also, the indicated output connections are floated, i.e.,they avoid signal ground connections. This is very practical for resetoperations. An important aspect of the circuit hereof is that thesuccessive switching between control branches T and T through theflip-flop (40) action eliminates transformer recovery time as a factorin repetition rate. The control signals or pulses impressed upon load 20are as rapid as the transistors T and T can function.

Successive pulses, closely spaced, of the order of 2 to 3 microsecondslong have been practically controlled and impressed upon inhibit Windingloads (20). In fact due to the load sharing feature of this invention,the transistors T and T cool off and recover at least for alternatepulses, and relatively inexepnsive germanium-type units are adequate forsuch rapid repitition rates. Similarly, no expensive design orconstruction for the output transformers 21 and 22 is requisite. Asingle transformer with a center-tapped primary may be used in place oftwo transformers 21 and 22. Where a common directional output isrequired, two secondary windings are used corresponding to windings 53and 46 for an inhibit winding load.

Particularly practical advantages also accrue to the power supply (25)for the invention system. One important aspect is substantial uniformityof system loading or current drain on the power supply 25, regardless ofthe control status or mode of operation of the control circuitry. Thecurrent i from terminal 27 through resistor 3t) can be steered atcircuit point a into input branch T and i or into control lead 37 as 2'Proportioning the T branch elements and parameters is preferred, so thatits current i when flowing, is made substantially equal in magnitude to1' i and i when flowing. In this way current f remains constantregardless of whether T T or T is On.

The invention circuitry thus controls or steers a steady output currenti from power supply 25 in resistor 30 from standby branch T into eithercontrol branch T and T The currents i i or i can only occurindependently of each other in the circuit. The control or circuitcurrent steering rate is of the order of 0.2 to 0.3 microsecond,dependent upon the speed of the respective transistors T T and T mainly.Such switching rate is practically instantaneous. Thus, there isnegligible ripple in the power supply (25) loading by this circuitry;the load current (i is substantially constant at terminal 27, as Well asat converging point 0 to the V terminal 23. The power supply (25) avoidsswitching transients, and has "a simple, economical, filteringrequirement.

While the present invention has been described in connection with anexemplary circuit form and use, it is to be understood that variationsand modifications as to its arrangement and applications may be made bythose skilled in the art within the broader spirit and scope of theinvention as set forth in the following claims.

I claim:

1. An electrical switching system comprising a first transistor with animpedance, a pair of transistors, output transformer means in circuitwith'electrodes of said transistor pair, other electrodes of saidtransistor pair being coupled to said impedance for control actuationthereby upon current drop-off condition of said first transistor, meanscoupled to said transistor pair for alternately switching the capabilityof current passage through the transistors of said pair, and controlmeans in circuit with said first transistor for impressing controlsignals to substantially reduce the current therethrough incorrespondence therewith and effect redirection of the first transistorcurrent into said transformer means through the alternately operabletransistors of said pair.

2. An electrical switching system comprising a first transistor circuitwith a load impedance connected to a power supply source, a pair ofcontrol transistors, output transformer means in circuit with likeelectrodes of said transistor pair, a second like set of electrodes ofsaid transistor pair being connected to said impedance for controlactuation thereby upon current cut-oif condition of said firsttransistor circuit, bistable means coupled to a third like set ofelectrodes of said transistor pair for alternately switching thecapability of current passage through the transistors of said pair, andcontrol means in circuit with said first transistor circuit forimpressing control signals to cut-0E the current therethrough incorrespondence therewith and eifect redirection of the first transistorcircuit current intosaid transformer means through the alternatelyoperable transistors of said pair.

3. An electrical switching system comprising a standby transistorcircuit with a load resistor connected to a power supply source, a pairof control transistors, output transformer means in circuit withelectrodes of said transistor pair, other electrodes of said transistorpair being connected directly to said resistor for control signalactuation thereby upon current cut-off condition of said standbytransistor circuit, bistable means coupled to said transistor pair foralternately controlling the capability of current passage through thetransistors of said pair, and control means in circuit with said standbytransistor for impressing pulsed control signals to cut-off the standbycurrent therethrough in correspondence therewith and effect redirectionof the standby transistor circuit current into said transformer meansthrough the alternately operable transistors of said pair, whereby thecurrent loading on the power supply remains substantially constantduring system switching operations.

4. An electrical switching system comprising a standby transistorcircuit with a load impedance connected to a DC. power supply source,said transistor circuit being proportioned to normally conduct apredetermined current through said impedance, a pair of controltransistors, output transformer means having two primary windings eachin circuit with like electrodes of said transistor pair, a second likeset of electrodes of said transistor pair being coupled to saidimpedance for control signal actuation thereby upon current reductioncondition of said standby transistor circuit, bistable means coupled tothe third electrodes of said transistor pair for alternately switchingthe capability of current passage through the transistors of said pair,and control means in circuit with said standby transistor for impressingcontrol signals to substantially reduce the standby current therethroughin correspondence therewith and eifect redirection of the stand bytransistor circuit current into said transformer windings through theassociated alternately operable transistor of said pair, whereby thetransistors of said pair effectively share the load of the outputcontrol operation.

5. An electrical switching system as claimed in claim 1, in which saidcontrol means is an AND circuit with a plurality of control inputs.

6. An electrical switching system as claimed in claim 2, in which saidcontrol means is an AND circuit with a plurality of control inputs andsaid bistable means is a flip-flop unit with substantial voltage outputsfor its switchin g function.

7. An electrical switching system as claimed in claim 4, in which saidbistable means is a flip-flop unit with substantial biasing controlvoltage outputs for its switching function.

8. An electrical switching system as claimed in claim 1, in which saidoutput transformer means includes two transformers in individual circuitwith a transistor of said pair, whereby each transformer shares theoutput loading and fully recovers in its signal translating capabilitybetween successive signal conditions.

9. An electrical switching system as claimed in claim 3, in which saidoutput transformer means includes two pulse transformers with theirprimary windings in individual circuit with a transistor of said pairand a common current return path to the power supply.

10. An electrical switching system as claimed in claim 2, in which saidoutput transformer means includes two transformers with their primarywindings in individual circuit with a transistor of said pair, and thesecondary windings of said transformers being interconnected for commonoutput signal phasing to the load, whereby each transformer shares theoutput loading and fully recovers in its signal translating capabilitybetween successive signal conditions.

11. An electrical switching system as claimed in claim 4, in which saidoutput transformer means includes two pulse transformers with theirprimary windings in individual circuit with a transistor of said pairand a common current return path to the power supply, and the secondarywindings of said pulse transformers being interconnected for commonoutput signal phasing to the load with diodes in circuit therewith toprevent winding interaction, where each pulse transformer shares theoutput loading and fully recovers in its signal translating capabilitybetween successive signal conditions.

12. An electrical switching system comprising a first transistor circuitwith an impedance, said first transistor circuit being and normallybiased to have a predetermined standby current flow, a second circuitcontaining a plurality of transistors and a load element connected to afirst electrode of each of the transistors thereof, a second electrodeof each of said transistors being coupled to said impedance for controlactuationby said first circuit means connected to each of saidtransistors for selectively controlling their conducting capability, andcontrol means coupled with said first transistor circuit for impressingcontrol signals thereon to effect an input control on said secondelectrodes and effectively redirect the standby current through thetransistor that is coincidentally controlled by said means and therebyinto its associated load element.

13. An electrical switching system comprising a first transistor circuitwith an impedance and normally biased to have a predetermined standbycurrent flow, a second transistor circuit containing a plurality oftransistors and a load element connected to a first like electrode ofeach of the transistors thereof, a second like electrode of each of saidtransistors being coupled to said impedance for control actuation bysaid first circuit, selective biasing means connected to a third likeelectrode of each of said transistors for selectively controlling theirconducting capability, and control means coupled with said firsttranssistor circuit for impressing control signals thereon thatsubstantially cut-01f its standby current flow to effect an input:control of said second like electrodes of said second transistorcircuit and effectively redirect the standby current through thetransistor of said second transistor circuit that is coincidentallycontrolled by said selective biasing means and thereby into itsassociated load element.

References Cited in the file of this patent UNITED STATES PATENTS2,881,332 Jensen Apr. 7, 1959

4. AN ELECTRICAL SWITCHING SYSTEM COMPRISING A STANDBY TRANSISTORCIRCUIT WITH A LOAD IMPEDANCE CONNECTED TO A D.C. POWER SUPPLY SOURCE,SAID TRANSISTOR CIRCUIT BEING PROPORTIONED TO NORMALLY CONDUCT APREDETERMINED CURRENT THROUGH SAID IMPEDANCE, A PAIR OF CONTROLTRANSISTORS, OUTPUT TRANSFORMER MEANS HAVING TWO PRIMARY WINDINGS EACHIN CIRCUIT WITH LIKE ELECTRODES OF SAID TRANSISTORS PAIR, A SECOND LIKESET OF ELECTRODES OF SAID TRANSISTOR PAIR BEING COUPLED TO SAIDIMPEDANCE FOR CONTROL SIGNAL ACTUATION THEREBY UPON CURRENT REDUCTIONCONDITION OF SAID STANDBY TRANSISTOR CIRCUIT, BISTABLE MEANS COUPLED TOTHE THIRD ELECTRODES OF SAID TRANSISTOR PAIR FOR ALTERNATELY SWITCHINGTHE CAPABILITY OF CURRENT PASSAGE THROUGH THE TRANSTORS OF SAID PAIR,AND CONTROL MEANS IN CIRCUIT WITH SAID STANDBY TRANSISTOR FOR IMPRESSINGCONTROL SIGNALS TO SUBSTANTIALLY REDUCE THE STANDBY CURRENT THERETHROUGHIN CORRESPONDENCE THEREWITH AND EFFECT REDIRECTION OF THE STANDBYTRANSISTOR CIRCUIT CURRENT INTO SAID TRANSFORMER WINDINGS THROUGH THEASSOCIATED ALTERNATELY OPERABLE TRANSISTOR OF SAID PAIR, WHEREBY THETRANSISTORS OF SAID PAIR EFFECTIVELY SHARE THE LOAD OF THE OUTPUTCONTROL OPERATION.